Nonvolatile memory cells having a charge trapping layer to store charges is well known in the art. See for example, U.S. Pat. No. 6,940,125 assigned to the present assignee, whose disclosure is incorporated by reference in its entirety herein. Bi-directional cells made from trenches in a substrate are also well known in the art. See U.S. Pat. Nos. 6,940,125 6,861,315 and 6,936,883. Finally, the use of silicon nanocrystals (Si-nc) embedded in SiN as a charge trapping layer is also well known in the art. See Choi S., et al. “High Density Silicon Nanocrystal Embedded in SiN Prepared by Low Energy (<500 eV) SiH4 plasma Immersion Ion Implantation for Non-volatile Memory Applications” IEDM August, 2005.
It is an object of the present invention to provide a bi-directional non-volatile memory cell (as well as an array and a method of making the array) using a charge trapping layer to store multi-bits in each cell.